Many applications, usually involving either mounting parts or routing wiring and other materials, require holes to be drilled or punched into sheet metal. As with any other typical fabrication task, there isn't always a right or wrong way to do the job. But, sometimes there is a better way. We're going to discuss several methods to drill and punch holes in sheet metal. Some of these methods can be used interchangeably, but this depends on the application the hole needs to be created for, the size of the hole and the requisite tooling costs.

Once the hole centers are marked with ink or scribed crosshairs, use a center punch to strike each location. The dimples left by the center punch serve to guide drill bits and punch tips to prevent them from walking or wandering across the sheet metal surface.

Automatic and spring-loaded center punches are quick and handy to use, but a set of manual punches and a ball peen hammer offer more flexibility.

Step 2: Always Use a Clamp—or Three

Never ever hold a sheet-metal workpiece in your hands when drilling, and always clamp it down when you can. When setting up clamps or hold-downs, anticipate that a drill bit will catch and grab the workpiece, and adjust your clamps to ensure that the metal cannot spin. What do you get when spinning sheet metal meets human flesh? A bad day if you're lucky, a trip to the hospital if you're not.

Before you clamp down your workpiece, consider masking the back of the sheet with tape to help control and prevent tearout. If the sheet is to be clamped to a sacrificial wooden board for the same reason, masking is not necessary. If your workpiece surface is easily marred or already finished, consider masking the front and back of it anyway, just in case.

Step 3: Twist Drills are Great for Small Diameter Holes

Drilling a hole in sheet metal with a twist drill is a rather straightforward operation. You start off by drilling a small diameter pilot hole, and then drill gradually larger holes until you get to the size you need. This method works for small-diameter holes but it can be tedious and time-consuming when the project calls for numerous holes, large holes or numerous large holes.

Step 4: Using a Step Drill Bit to Skip Some Steps

Step drill bits, such as the venerable Unibit, can drill several hole sizes in a single operation. These single-flute bits are specially designed for thin materials, and feature steps of progressively larger diameters.

Self-starting step bits do not require any pilot holes to be drilled, and can create large burr-free holes in the blink of eye. Step bits can be used to make even larger holes (typically 1-3/8-inch wide or smaller) in sheet metal, but do require pilot holes. It is common practice to use a self-starting step bit to form the large pilot hole needed for a hole-enlarging step bit.

Step 5: Hole Saws for Large Opening

In contrast to how twist and step drill bits operate, hole saws work by cutting out the edges of an opening. Metal-cutting hole saws are typically available in 3/4-inch to 6 inches in size, and feature a sawtooth-tipped cylinder with a pilot drill bit at its center. Some hole saws have permanently fixed arbors and pilot bits; others are modular and must be assembled.

Not only is a backer board a good idea for reducing tearout, but it helps guide a hole saw's pilot bit, keeping the tool aligned. When using larger saws on tougher material (such as steel), cutting fluid can help make the job go easier and prolong the saw's life. Manufacturers will usually provide a table of recommended rpms according to hole size and the material being cut.

As with ordinary drill bits, hole saws can sometimes bind, and when they do they can grab a workpiece with a lot of force. If using a handheld drill on a well-clamped workpiece, position your grip and body so that the drill won't smack you should it grab the workpiece and torque out of your hands.

Step 6: Portable Hand Punches—No Mess, Lots of Grip

A hand punch, such as those by Roper Whitney, can be used to make perfect holes in sheet metal quickly and with relatively little effort. For larger holes or use on thicker gauges of steel, more robust and costlier bench-mounted punches may be required.

To use a portable hand punch, first select and install a matching punch and die set. Align the point of the punch over a soon-to-be-hole's center, and squeeze the tool's handles together. Once the punch clears through the sheet, a small slug will drop free and then the tool can be removed. Punched holes have relatively clean edges that require little to no finishing.

Step 7: Knockout Punches Wield Sheer Force

Knockout punches, such as Greenlee's ubiquitous Slug-Buster, can be used to make holes much larger than a portable hand punch can handle. Commonly used by electricians to punch holes for conduit, knockout punches are easy to use and provide great results, but larger sizes are prohibitively expensive.

A knockout punch consists of three parts: a draw stud, punch and die. To setup the punch, first drill a pilot hole into a piece of sheet metal with a step drill bit. Place the die over the draw stud before inserting the stud through the pilot hole. The punch is then threaded onto the tip of the draw stud and brought close to the sheet metal. A socket or wrench is then used to turn the draw stud, gradually pulling the punch through the sheet metal and into the die. Once the punch is completely pulled through, the hole is complete and the punch can be removed from the stud.

Knocked-out holes typically require a bit of deburring, but not as much as holes cut with hole saws do.

Step 8: Circle-Cutters for Large or Odd-Sized Holes

When drilling or punching a hole in sheet metal, you more or less cut out the entire hole at once. When cutting out a circle, one or sometimes two cutting tools are rotated about a center point to form a hole.

The circle cutter you see here, by General Tools, is designed to be used with a drill press. To use it, set the radius between the pilot bit and cutter to correspond with the hole you need to make. Since this circle cutter is not completely balanced, it can be unstable or even dangerous to use.

For cutting large holes without a drill press, circle-cutter attachments are also available for Dremel and RotoZip-style rotary tools.

Step 9: A Smooth Finish

While some holes in sheet metal may be cut very cleanly, most will require slight finishing for best results. Certain applications may call for grommets or rubber trim to be inserted in or over the holes, in which case this step can be skipped.

There are several ways to clean up and deburr a newly drilled or punched hole. For small holes, a gentle finger-twist of a slightly larger-size twist drill over the hole is usually enough to break down any sharp edges. For the deburring of larger holes, a handheld deburring tool offers the quickest and easiest way to clean up jagged edges.

To use a deburring tool, rest the tool's sharp blade against the edge of a newly made hole and drag it around with a circular motion. The deburring blade will self-adjust itself as it removes a thin layer of material from around the hole.